Android代码报‘Class, Interface or Enum Expected’错误求助排查

Let's break down the small but critical issues causing that frustrating error in your code—they're easy to miss but simple to fix:

1. Typo in SeekBar Listener Import #

You have a lowercase b in Seekbar here:

import android.widget.Seekbar.OnSeekBarChangeListener;

Android's class name is SeekBar (capital B), so correct the import to:

import android.widget.SeekBar.OnSeekBarChangeListener;

2. Mismatched Superclass Import & Declaration #

You imported AppCompatActivity but your class extends Activity:

import android.support.v7.app.AppCompatActivity;
// ...
public class MainActivity extends Activity {

Since you're using the support library import, update the class declaration to match:

public class MainActivity extends AppCompatActivity {

If you intended to use the base Activity class instead, add the corresponding import:

import android.app.Activity;

3. Misplaced Listener Definitions & Extra Closing Braces #

You defined your SeekBar.OnSeekBarChangeListener and TextWatcher inside the calculate() method, which is invalid syntax for Java—these need to be top-level members of your class. Your code also has an extra closing brace at the end that breaks the class structure entirely.

Corrected Full Code #

Here's the fixed version with all issues resolved, plus small tweaks for modern Android Studio:

package com.example.chigh.tipcalculator; 
import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.text.Editable; 
import android.text.TextWatcher; 
import android.widget.EditText; 
import android.widget.SeekBar; 
import android.widget.SeekBar.OnSeekBarChangeListener; 
import android.widget.TextView; 
import java.text.NumberFormat; 

public class MainActivity extends AppCompatActivity { 
    private static final NumberFormat currencyFormat = NumberFormat.getCurrencyInstance(); 
    private static final NumberFormat percentFormat = NumberFormat.getPercentInstance(); 
    private double billAmount = 0.0; 
    private double percent = 0.15; 
    private TextView amountTextView; 
    private TextView percentTextView; 
    private TextView tipTextView; 
    private TextView totalTextView; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.activity_main); 

        // Initialize views (no explicit cast needed in modern Android Studio)
        amountTextView = findViewById(R.id.amountTextView); 
        percentTextView = findViewById(R.id.percentTextView); 
        tipTextView = findViewById(R.id.tipTextView); 
        totalTextView = findViewById(R.id.totalTextView); 

        tipTextView.setText(currencyFormat.format(0)); 
        totalTextView.setText(currencyFormat.format(0)); 

        EditText amountEditText = findViewById(R.id.amountEditText); 
        amountEditText.addTextChangedListener(amountEditTextWatcher); 

        SeekBar percentSeekBar = findViewById(R.id.percentSeekBar); 
        percentSeekBar.setOnSeekBarChangeListener(percentSeekBarListener); 
    } 

    private void calculate() { 
        percentTextView.setText(percentFormat.format(percent)); 
        double tip = billAmount * percent; 
        double total = billAmount + tip; 
        tipTextView.setText(currencyFormat.format(tip)); 
        totalTextView.setText(currencyFormat.format(total)); 
    } 

    // Define SeekBar listener as a class member
    private final SeekBar.OnSeekBarChangeListener percentSeekBarListener = new SeekBar.OnSeekBarChangeListener() { 
        @Override 
        public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) { 
            percent = progress / 100.0; 
            calculate(); 
        } 

        @Override 
        public void onStartTrackingTouch(SeekBar seekBar) { } 

        @Override 
        public void onStopTrackingTouch(SeekBar seekBar) { } 
    }; 

    // Define TextWatcher as a class member
    private final TextWatcher amountEditTextWatcher = new TextWatcher() { 
        @Override 
        public void beforeTextChanged(CharSequence s, int start, int count, int after) { } 

        @Override 
        public void onTextChanged(CharSequence s, int start, int before, int count) { 
            try { 
                billAmount = Double.parseDouble(s.toString()) / 100.0; 
                amountTextView.setText(currencyFormat.format(billAmount)); 
            } catch (NumberFormatException e) { 
                amountTextView.setText(""); 
                billAmount = 0.0; 
            } 
            calculate(); 
        } 

        @Override 
        public void afterTextChanged(Editable s) { } 
    }; 
}

Quick Modernization Note #

If you're using AndroidX (recommended for new projects), replace the support library import with:

import androidx.appcompat.app.AppCompatActivity;

内容的提问来源于stack exchange，提问作者Casey Hight